Amide oxidation inhibitor for lubricants



United States Patent 3,260,671 AMIDE OXIDATION INHIBITOR FOR LUBRICANTS Robert T. Trites and Phillip A. Froehlich, Cincinnati,

Ohio, assignors to Emery Industries, Inc., Cincinnati,

Ohio, a corporation of Ohio No Drawing. Filed Nov. 23, 1962, Ser. No. 239,812

9 Claims. (Cl. 25251.5)

This invention relates to a novel composition which is particularly effective when used as an oxidation inhibitor in a jet engine lubricant. Briefly described, the invention relates to compounds comprising amides of the type formed by reacting a higher aliphatic, saturated, branched chain monocarboxylic acid with an amine containing both a tertiary as well as a primary amine group. The invention also relates to various lubricant compositions containing said amides.

Oxidation inhibitors are added to lubricant fluids to minimize oxidative decomposition of the fluid to acid products which tend to form sludge and to corrode the various metal surfaces with which the lubricant comes into contact. This service demand imposed on the oxidation inhibitor increases rapidly with engine temperatures. Thus, many of the agents which give adequate protection at temperautres such as 300 F. have substantially no utility at higher temperatures. The lubrication of the gas turbine engines utilized in aircraft propulsion is an excellent illustration of this point. In 1953 the commercial aircraft gas turbine power plant was operated at approximately 300 F. maximum temperature, using a petroleum lubricant and a classic oxidation inhibitor such as an alkylated phenol. However, since 1953 the gas turbine engines have been designed for higher performance ratings. This has necessitated raising the operating temperatures from 300 F. to 350 F., then 400 F., and now to designs which require lubricant stability up to 450 F. At temperatures above 300 F. the classic oxidation inhibitors fail to perform the required function.

It is an object of the present invention to provide a novel class of compounds which effectively inhibit oxidation of lubricant compositions at temperatures above 300 F. A further object is to provide a material of this character which is readily soluble in both hydrocarbon as Well as synthetic lubricants, and which does not appreciably affect the liquidous characteristics of the base fluid. A still further object is to provide stable lubricant compositions which can be employed with good results at temperatures of from about 300 to 450 F. or even higher. The nature of other objects of the invention will be apparent from a consideration of the descriptive portion to follow.

The present invention rests on the discovery that the foregoing objects can be achieved through use of a novel amide of the type having the general formula R1 0 II N( 0 H2) 2-5-NH-C Rr Ra where R represents a C C, alkyl radical such as methyl, ethyl, propyl, butyl or isobutyl; R represents a branched chain, saturated aliphatic hydrocarbon group of from about 15 to 24 carbon atoms, this group being, in effect, the hydrocarbyl or non-carboxy portion of a normally liquid, branched chain, saturated, aliphatic monocarboxylic acid containing from about 16 to 25 carbon atoms; and R is a radical selected from the group consisting of those represented by R in the above formula and by the portion of said formula.-

The amide oxidation inhibitors of this invention have unusually good solubility characteristics and are miscible in all proportions with ester type lubricants, polyglycol lubricants and petroleum base oils without appreciably affecting the liquidous range of the base lubricant. Further, these amide additives are highly stable and are adapted to be employed with any of the conventional additives Which are used in formulating a lubricant intended for high temperature service.

The amide compounds disclosed herein are prepared in conventional fashion by heating together stoichiometrically equivalent amounts of the carboxylic acid and amine reactants, as hereinafter defined. Preferably an excess of the amine is used, the better to drive the reaction to completion, with any excess amine then being stripped from the finished reaction mixture. This amidation step, which is conducted at temperatures of about to 225 C. until the reaction is complete as indicated by the evolution of the theoretical amount of water of reaction, is preferably carried out in the presence of a suitable solvent such as xylene or toluene which forms an azeotrope with the evolved water. The reaction mixture is given a final stripping in vacuo to remove any remaining solvent and excess amine. The residual amide is substantially neutral and typically has an acid value of less than 2. In a representative preparation, one mole of a C saturated, branched chain, monocarboxylic fatty acid is reacted with 1.2 moles of an amine such as N,N-dimethylaminopropyl amine to form the amide. Were the amine reactant to be one such as N-methyl-bi-s(aminopropyl) amine, which contains two primary amino groups, then 2 moles of the acid would have been employed along with about 1.2 moles of the amine. The excess of the amine utilized in the preparation normally ranges from about 5 to 30% for optimum results.

The monocarboxylic acid employed to form the amide is, as stated above, one which contains from about 16 to 25 carbon atoms and has a branched chain structure. Acids of this character are conventionally liquid at room temperatures and are prepared by synthetic methods. A typical acid adapted to be used in the preparation of the present amides is one containing 18 carbon atoms which is formed from a by-product obtained on polymerizing naturally occurring unsaturated fatty acids in accordance with the method described in U.S. Patent No. 2,812,342. According to the disclosure of said patent, monounsaturated or polyunsaturated fatty acids are treated thermally in the presence of water with or without a catalyst or clay to produce products which are known commercially as dimer acids. This process inherently produces a substantial amount of by-product which is a mixture of monomeric acids. This monomer mixture, which is normally distilled in vacuo from the polymer-containing reaction product, includes saturated fatty acids which have not been affected by the polymerization treatment, probably some unsaturated fatty acids which have not been affected by the polymerization treatment and fatty acids which have been structurally modified by the polymerization treatment in such a manner that they resist further polymerization.

According to Patent No. 2,812,342 the recovered mixture of monomeric fatty acids is hydrogenated to reduce the iodine value of the mixture to a level below 10 and perhaps as low as 3, thereby reducing any natural unsaturated fatty acids which may be present to saturated fatty acids. The hydrogenation treatment also reduces the iodine value of the fatty acids. which have been structurally modified in some degree by the polymerization treatment. It is difficult to estimate the additional degree of structural modification, if any, which takes place during hydrogenation.

The hydrogenated fatty acid mixture is then solvent separated to remove solid fatty acids such as stearic and palmiti-c acids. The remaining saturated fatty acids are all structurally modified products which, While containing 18 carbon atoms, possess a branched chain structure, a titre below 15 C., and an iodine value of substantially 3 to 10.

In manufacuring C acids for use in forming the amides of this invention, the above described process must be practiced very carefully to effect the best possible segregation of the different classes of acids. For instance, if the hydrogenation process is practiced inelfectively, then oleic acids will show up as an impurity in the end product. The presence of oleic acid in the final product is undesirable because oleic acid is not stable in the sense of being resistant to oxidation. Also, if the solvent separation operation is not practiced effectively, then stearic or other solid acids will be present, and lubricants which include amides of stearic acid will have an undesirably high pour point. In summary, the process of Patent No. 2,812,342 must be practiced with sufiicient care to recover the structurally modified acids without the presence of any objectionable quantity of the undesirable impurities.

While Patent No. 2,812,342 refers to the C fatty acids in question as structurally modified acids (which they are in relation to the starting materials), these acids are more aptly described as structurally stabilized acids. Thus, these acids have already received two very severe treatments, one a polymerization treatment which tends both to polymerize and to modify structurally the unsaturated acids, and the other a hydrogenation treatment which saturates and perhaps further modifies the structure of the acids. Hence, these structurally modified acids have become stabilized acids in the sense that they have been subjected to such rigorous treatment as to have developed their most stable structural form. While these acids may thus properly be termed structurally stabilized, C monocarboxylic acids, it also is appropriate to term them isostearic acids in view of their C branched chain structure. The latter terminology is employed herein in the interests of simplified, yet clear nomenclature.

Another normally liquid monocarboxylic acid which can be employed is that which contains 22 carbon atoms and is prepared by the polymerization of isobutylene with oleic acid. The resulting product, on being hydrogenated to effect saturation thereof, will consist essentially of a mixture of 9- and l-sec.-butylstearic acids. Still other normally liquid acids falling within the perimeter described for the monocarboxylic acid reactant will suggest themselves to those skilled in the art, e.g., 9-n-octylmargaric acid and IO-methylstearic acid, to name but .a few.

Typical amine reactants which can be used to prepare the amide anti-oxidant hereof include the following:

N,N-dimethyl-aminopropyl amine N,N-diethyl-aminopropyl amine N,N-diisopropyl-aminopropyl amine N-methyl-N-ethyl-aminopropyl amine N,N-dimethyl-aminoethyl amine N,N-dimethyl-aminobutyl amine N,N-dimethyl-aminopentyl amine N-methyl-bis(aminopropyl) amine N-methyl-N-aminopropyl-N-aminoethyl amine N-ethyl-bis(aminobutyl) amine N-propyl-bis(aminopropyl) amine N-isopropyl-bis(aminopropyl) amine N-methyl-N-aminopentyl-N-aminopropyl amine 0f the above amines, particularly good results are obtained with N,N-dimethyl-aminopropyl amine, and this compound is thus preferred. Similarly, the preferred acid reactant is the described C isostearic acid. Accordinglly, the preferred amideoxidation inhibitor is the resultant reaction product. N,N-dimethyl-isostearamidopropyl amine, Whose preparation is described in Example 1.

The amide anti-oxidants of this invention can be employed with good effect in connection with a wide variety of lubricant base stocks. Thus, the latter stock may be one of natural origin such as a highly refined or superrefined mineral oil, or it may be a synthetically prepared stock such as an ester or a polyglycol.

As regards the ester class of lubricants, the amides hereof can be used with any one or more of the wide variety of aliphatic, carboxylic acid esters which have been proposed for lubricant usage. Included in this group are the dialkyl (C C esters of aliphatic dicarboxylic acids (C c the principal diesters being those derived from adipic, azelaic or sebacic acid and a C to C10 alcohol.

Specific examples of the dialkyl esters of aliphatic dicarboxylic acids are di-isooctyl azelate, di-Z-ethylhexyl sebacate, -di-2-ethylhexyl adipate, dilauryl azelate, di-secamyl sebacate, di-'2-ethylhexyl alkenylsuccinate, di-2- ethoxyethy-l sebacate, di-2(2'-methoxyethoxy) ethyl sebacate, di-2-(2'-ethylbutoxy) ethyl sebacate, di-Z-ethylhexyl azelate, di-2-(2'- butoxyethoxy) ethyl alkenylsuccinate, etc.

In addition to the aliphatic dicarboxylic acid esters described above, polyester lubricants formed by a reaction of an aliphatic dicarboxylic acid, a glycol and a monofunctional compound, which is either an aliphatic monohydroxy alcohol or an aliphatic monocarboxylic acid, in specified mol ratios are also employed as the synthetic lubricating base. Complex esters formed by reaction of a rnixture containing specified amounts of 2-ethyl-l,3- hexanediol, sebacic acid and '2-ethyilhexanol and by reaction of a mixture containing adipic acid, or azelaic acid, diethylene glycol and 2-ethylhexanoic acid illustrate this class of synthetic polyester lubricating bases.

Polyesters formed by reaction of a monocarboxylic acid and a glycol may also be used as the ester component. The acid component is usually as aliphatic acid containing at least 6 carbon atoms. The glycol component can be a straight glycol such as 1,6-hexanediol, but ether glycols such as tetraethylene glycol or dipropylene glycol may also be used.

Specific examples of the diesters of glycols are the following: di-n-decanoate of l,44blutanediol, di-2-ethylhexanoate of 1,6-hexanediol, dilaurate of l,4-hexanediol, di-octanoate of 1,5-pentanediol, dilaurate of tetraethylene glycol, 'dilaurate of triethylene glycol, dioctoate of pentaethylene glycol and dipelargonate of dipropylene glycol. I Esters formed by reacting trimethylol alkanes (C -C with various monobasic acids, primarily C -C acids, comprise another example of esters useful for the base fluid of the lubricants of this invention.

The amount of amide oxidation inhibitor to be employed in a given lubricant will, of course, vary with the particular amide chosen, the nature of the lubricant fluid, and the service conditions to be encountered. However, good results are obtained as a general rule using amounts of about 0.2 to 5% of the amide, with a preferred range being from about 0.5 to 2%.

In addition to providing a given lubricant fluid with an amide of the type described herein, other additives may properly be employed as well. Thus, improved results are obtained by adding a metal deactivator such as PANA (phenyl-alpha-naphthylamine) along with the amides hereof. Other conventional additives can be used as Well, including those which impart rust inhibiting or load carrying qualities. It is also possible to incorporate an auxiliary oxidation inhibitor compound, if desired. Still another class of additives which can be em ployed, if desired, comprises those which impart improved V.I. characteristics to the composition.

The present invention is illustrated in various of its embodiments by the following examples.

EXAMPLE 1 This example describes the preparation of N,Ndimethyl-isostearamidopropyl amine. A solution was prepared from 30 grams of xylene and 2196 grams (1 mole) of isostearic acid. To this solution was added 120.4 grams 1.2 moles) of N,N-dimethy1-arninopropyl amine, addition of the amine being effected slowly (2-3 hours) as the solution was refluxed at 2002'10 C. The water of reaction was removed azeotropically under reflux by means of a water trap. After the addition of the amine was completed the material was allowed to reflux (200 C.) for six hours to distill off all possible water of reaction, the water being collected ina Banett trap. The reaction mixture was stripped to 120 C. under a vacuum of 1 mm. of mercury to remove the xylene and the excess amine. This stripping stage required one hour. The amide formed had an acid value of 1.2 milligrams of KO H per gram of sample.

EXAMPLE 2 In the same general fashion as described in Example 1 above, the isostearic acid (1 mole) was reacted with N,N-diethyl-aminopropyl amine (1J2 moles) to rform the corresponding amide, N,N-'diethyl-isostearamidopropyl amine.

EXAMPLE 3 Again using the same general method of preparation as set forth in Example 1, there was reacted 2 moles of the isostearic acid with 1.2 moles of N-methyl-bis (aminopropyl) amine. There was thus formed the compound N-methyl-bis (isostearamidopropyl) amine.

EXAMPLE 4 not effect an unduly pronounced change in the 'low temperature viscosity characteristics of the fluid.

Table 1 EFFECT OF AMIDE OXIDATION INHIBITOR ON LOM TEMPERATURE VISCOSITY OF ESTER BASE FLUIDS [1% amide of Example 1+0.5% PANA] Viscosity Ester Lubricant No Amide, With cs. Amide,

1 Di-(2-ethy1hexy1) Azelate 7,000 1 7, 620 2. Di-isooctyl Azelate 8, 500 1 10,911 3-.." TNEP 2 Dipelargonate Monoheptano- 3, 740 3 4, 533

2 TMP=Trimethylo1 Propane.

EXAMPLE 6 The amide of Example 1 was incorporated at the 1% level, along with 0.5% PANA, where indicated, in diisooctyl azelate. The resulting material was then subjected to oxidation-corrosion testing under MlL-L-7808E conditions, air being passed through the fluid at a rate of S l./ hr. as the fluid was maintained at 400 F. rather than 347 F., as called for by the specification. During the test copper, steel, aluminum and magnesium coupons were suspended in the test liquid. The results of this test are given in Table II below, it being noted that in contro run 1, the oxidation inhibitor employed was 0.5% phenothiazine, this being the conventional additive and corresponding level of the art.

Table II ACCELERATED MIL-L-7808E TEST [400 F., 5 l.-air/hr., 48-72 hrs., di-isooctyl azelate] Viscosity Corrosion Coupons Weight Change Sludge Change After Acid No. After 72 Hrs., Mg'./Sq. Cm. Oxidation Inhibitor System (Mg. after 48 Hrs. (Percent (Change after 48 Hrs.) at 100 F.) 48 Hrs.)

Cu Steel Mg Al 1 0.5% Phenothizaine 324 +20. 2 +13. 8 01 18 09 .16 2 1.0% Ex. 1 Amide 58 +3. 0 +4. 5 08 07 02 06 3 1.0% Ex. 1 Amide+0.5% PAN 79 +4.14 +1. 5 05 08 06 07 1 MIL-L-7808E calls for a weight change not exceeding +0.2 Mg./Sq. Cm. on all these metals after 72 hrs. 7

EXAMPLE 5 In the runs included in this example, the amide of EXAMPLE 7 The tests described in this example were conducted in accordance with the ,so-called celanese method, both in Example 1 was admixed with various ester base fluids its former version (4250 48 hrs, 96 L air/hr. Cu,

(as indicated in Table I) at the 1% wt. level. 0.5% wt. of PANA was also included in each formulation. From the viscosity data presented in the table it will be seen that incorporation of the indicated oxidation-inhibiting steel, Ag, Al, Mg and Ti coupons) and by the later modification involving 196 l. air/hr. for 18 hrs., other conditions remaining the same. In this test, the coupon weight change should not exceed :03 mg./sq. cm., and since and metal deactivation additives to the base fluid does all coupon weight changes fell within this range, they are not reported below in Table III which gives the other low temperature properties than the corresponding TMP test results. and TMB esters.

Table IIl.Celanese test, 425 F.

961. AIR/HR.-48 HOURS Vis. Change Acid N o. Sluge Ester Additive (percent at Change (Mg) TMP Dipelargonate Monoheptanoate. 1.5% Ex. 1 Amide, 0.5% PANA... +1.0 26 10. Same as 1 0.5% Phenothiazine 20. 0 +18. 0 116. 4

TM]? Triheptanoate 1.0% PANA, 1.0% -00 2 +523 1961. AIR/HR.18 HOURS 4 Same as 3 5 Heyden Newport TP-653B I Became solid. 2 l0l0=5 ethyl-10,10-diphenyl phenazasilane. 3 Believed to be a TMP ester formed from mixed C and C9 acid, average 0 EXAMPLE 8 We claim:

1. An amide having the general formula The tests described in th1s example were conducted under (Type II) conditions wherein 5 l. air/hr. is passed through the lubricant fluid for 48 hours, the fluid being at a temperature of 450 F. Metal coupons (Cu, steel, Ag, Al, Mg and Ti) are maintained in the fluid during the test, and their change in weight is determined. Each coupon may have a weight change not exceeding :03 mg./sq. cm. However, as a practical matter it has been found that of the various metals, magnesium is the most prone to attack under the extreme temperatures of this wherein R is a saturated branched chain aliphatic radical of 17 carbon atoms derived from isostearic acid.

2. A stabilized lubricant composition comprising a major portion of a lubricating oil, together with from 0.2 to 5% of an amide of the type having the general formula test. Hence, laboratory workers, in evaluating a fluid, frequently record only the magnesium weight change. (CH2)2-5NH-GR2 Again, they frequently extend the 48 hour test period until f the magnesium weight loss approaches the 0.3 mg. limit of the test. The data obtained from tests conducted under where R is an alkyl radical of from 1 to 4 carbon atoms, Type II conditions with various ester lubricant bases and R is a saturated, branched chain, aliphatic hydrocarbon with several amides (those of Examples 1-4 hereof) as radical of from about 15 to 24 carbon atoms, and R is a well as non-amide oxidation inhibitor systems, are pre radical selected from the group consisting of those repsented below in Table IV. resented by R in the above formula and by the portion Table IV [Type 11 test, 450 F., 51. air/hr., 48 hrs. (or more)] Viscosity Mg. Coupon, Ester Additive Change Acid No. Sludge Wt. Change (Percent at Change (Mg) (Mg/Sq. Cm.)

TMP Dipelargonate Monoheptanoate 1.5% Ex. 1 Amide, 0.5% PANA. +21 +5. 3 577 +.16 (48 hrs.). TMP Triheptanoate 1% 10-10, 1% P ANA +520 +3. 3 1, 365 15.8 (48 hrs.). TM]? Dipelargonate Monoheptanoate 1.5% Ex. 2 Amide, 0.5% PANA 1hrs.).

. s. Same as 3 3.0% Ex. 3 Amide, 0.5% PANA +.25 (48 hrs.). Same as 3 1.5% Ex. 4 Amide, 0.5% PANA 17 (48 hrs.). TMP Dipelargonate lvlonoisodecanoate 1.5% Ex. 1 Amide, 1.0% PANA +.19 (120 hrs.).

It is evident from a consideration of the data represented above that tri-esters of trimethylol propane (TMP) with branched and/ or straight chain, monocarboxylic, aliphatof Said formula ic saturated acids of from about 5 to 10 carbon atoms 3 The lubricant of claim 2 wherein the lubricant are particularly well adapted to be used in high temterial is an aliphatic carboxylic acid ester Denimre l lublficant applicationsfrom a 4. The lubricant of claim 2 wherein the lubricant mastability standpoint, these ester compounds seem to r terial is a dialkyl ester'of an aliphatic dicar-boxylic acid spond Particularly Well to compoundmg Wlth the amldes having from 6 to 10 carbon atoms and an alcohol having of this invention, thus providing stabilized lubricant fluids f to 10 carbon w Which c either be used as such in the Presence of 5. The lubricant of claim 2 wherein the lubricant masuch other additives as may be incorporated in the sysi l is a di t l l m tem. While the data here under consideration revolve 6 Th l b i t f l i 2 h i h l b i about the use of TMP esters, generally similar results can t i l is an ester of a polyalkylene glycol and an aliphatic be obtained with esters of the closely related compounds, monocarboxyfic id trimethylol ethane, and trimethylol butane, it being recog- 7. The lubricant of claim 2 wherein the lubricant manized that the TMB esters would be somewhat poorer in terial is dipropylene glycol dipelargonate.

8. The lubricant of claim 2 wherein the lubricant material is a triester of a trimethylol alkane and at least one aliphatic, monocarboxylic acid of the group consisting of straight chain and branched chain acids containing from about 5 to 10 carbon atoms.

9. The lubricant of claim 2 wherein the lubricant material is a triester of trimethylol propane and at least one aliphatic, monocarboxylic acid of the group consisting of straight chain and branched chain acids containing from about 5 to 10 carbon atoms.

References Cited by the Examiner UNITED STATES PATENTS Cook et al 260404.5 White et a1. 44-66 Bell et a1. 260-4045 Lindstrom et a1. 44-66 Keller 260--404.5 Niedzielski 44-66 Newallis et 'al. 1 6722 DANIEL E. WYMAN, Primary Examiner. E. W. GOLD-STEIN, Examiner. L. G. XIARHOS, Assistant Examiner. 

2. A STABILIZED LUBRICANT COMPOSITION COMPRISING A MAJOR PORTION OF A LUBRICANT OIL, TOGETHER WITH FROM 0.2 TO 5% OF AN AMIDE OF THE TYPE HAVING THE GENERAL FORMULA 